The present invention relates to an apparatus for filtering liquid samples to effect microbiological analysis thereof.
Bacteria, mold and especially yeast are a permanent threat to the quality, stability and taste of liquids, including drinks, medicines and cosmetics. They are found in practically all environments including in the raw materials, on the surfaces of apparatus and in the air. mold cannot grow in non-alcoholic drinks once the manufacture is completed, but they can prosper in water and in sugar syrups, in which they cause strong smells and a disagreeable taste. High bacteria counts in the finished product indicate non-hygenic packaging that requires modification. The characteristic aspects of contamination by yeast are a white deposit at the bottom of the container as well as changes in taste and smell.
The preferred method for preventing the development of contamination, which represents a risk to the consumer and to the quality of the product, is to adopt a program of regular sampling and testing at key points in the production system. A systematically executed program of sampling and analyses enables the manufacturer to contain and remedy any such contamination at the source before it develops into a major problem.
Currently there are available many types of single use or reusable apparatus for carrying out this type of sampling and analysis, with a greater or lesser degree of ease of use.
The method most commonly used at present and recommended by French and US standards entails clamping a 47 mm diameter circular filter membrane having a pore size of 0.45 .mu.m between the smooth edges of a funnel and a circular support having a porous central surface, placing this filter system on a vacuum manifold or conical flask, pouring the sample into the funnel and vacuum filtering it to recover any microorganisms on the membrane. After filtration the funnel is rinsed with distilled water or a phosphate buffer to recover all of the microorganisms and to eliminate from the filter membrane itself any bacteriostatic agents which could falsify the results. The filter membrane is then removed, placed on a culture medium specific to the microorganism under test and allowed to incubate. After a specific incubation period, colonies form on the surface of the filter that are easy to count and identify. A major difficulty of this known method is manipulating the extremely fragile filter membrane, especially when detaching it from the support after filtration. When it is wet it is in perfect contact with the support, whose peripheral surface is generally coated with polytetrafluoroethylene to reduce the adhesion of the membrane to its support. However, it is still difficult to detach it from the support and especially to grasp it by its edge using tweezers without damaging it or deforming it during handling.